The present invention relates to bearings having hard, wear resistant surfaces such as ceramic bearings, and more particularly to an improved lubrication system for such bearings.
The invention is particularly suitable for oscillatory bearings such as airframe bearings used, for example, in aircraft and hydrofoils for control surface pivotal bearings and similar purposes, although this invention is equally applicable to other types of bearings where similar operating conditions may exist. Such bearings are subject to oscillatory operation under loads which in many cases are very high and which may be either unidirectional or reversing. Since the loads frequently exceed the capability of anti-friction bearings, plain slider bearings are usually used, and in many cases the bearings are subject to misalignment during operation making it necessary to use spherical or self-aligning types of slider bearings.
Bearings for this type of service preferably have hard, wear resistant bearing surfaces and ceramic materials are very desirable for this purpose because of their relatively inert characteristics, high hardness and ability to be machined to a smooth surface. Ceramic materials or other such hard materials, however, require lubrication to reduce friction and to eliminate or minimize wear between engaging surfaces. Solid lubricants are very suitable for this purpose and a thin film of lubricant coated on the engaging surfaces results in very low friction and can substantially eliminate wear. The life of such a thin film, however, is of relatively short duration and since an oscillatory bearing does not inherently distribute lubricant over the bearing surfaces in the manner of a continuously rotating bearing, means must be provided for maintaining the necessary lubrication between the engaging bearing surfaces.
In some conventional slider bearing designs, a lubricant liner has been utilized made of a lubricant such as polytetrafluoroethylene (TEFLON) fabric, or other material having similar lubricating properties. The load capacity of such bearings is severely limited, however, by the compressive strength of the liner material. Such liners are also subject to rapid wear and in many cases the wear rate is greater than can be permitted. Bearings have also been proposed in which lubricant is supplied in response to heating caused by friction as shown, for example, in patents to Vigne U.S. Pat. No. 1,941,768, Dalzell et al. U.S. Pat. No. 3,206,264 and Campbell et al. U.S. Pat. No. 3,509,957. These systems, however, all utilize fusible or metallic lubricant materials and are not suitable for the type of bearing applications to which the present invention is directed.